1. Field of the Invention
The present invention relates to an ink composition for use in an ink jet recording device and an ink jet recording method and an ink jet recording device using the same. More particularly, it is concerned with a hot-melt ink composition, which is solid at room temperature and jetted as droplets at a temperature above room temperature, and an ink jet recording method and an ink jet recording device using the same.
2. Background Art
Ink jet recording is excellent in noiselessness during recording and high speed printing. Liquid ink compositions containing water as a base have hitherto been used as an ink composition for ink jet recording. This type of printing, however, had a drawback that a remarkable difference in the quality of prints occurs between the kinds of paper. For this reason, hot-melt ink compositions have been proposed as an ink composition capable of realizing a good quality of print independently of the quality of the paper (U.S. Pat. Nos. 3,653,932, 3,715,219, 4,390,369, 4,484,948 and 4,659,383 and Japanese Patent Laid-Open Nos. 54368/1980, 113462/1981, 113472/1981 and 108271/1983). A recording method using this type of ink comprises heat-melting the ink composition, which is solid at room temperature, at a high temperature, jetting and putting droplets of the melted ink composition on a recording medium, and cooling and solidifying the droplets to form a record dot.
Although the conventional hot-melt ink compositions are excellent in the compatibility with the recording medium and in dryability after printing, they have had several problems. For example, since the record dot solidifies in a mound shape on the recording medium the strength of bonding between the record dot and the recording medium is so low that the record dot is peeled off by the action of external abrasion, heat, pressure and the like, that is, the conventional hot-melt ink compositions have poor abrasion resistance. Furthermore, it has been pointed out that, when the print is allowed to stand at a high temperature, it unfavorably sticks to a material put on the print (blocking) or blurs.
In order to avoid the problems, several methods have been proposed for successfully fixing the record dot to the recording medium by taking advantage of heat or pressure (U.S. Pat. No. 4,745,420 and Japanese Patent Laid-Open No. 205241/1988). In these methods, however, when the conventional hot-melt ink composition is employed, the ink composition unfavorably penetrates and diffuses into the recording medium during remelting, which often gave rise to blurring of the print. Furthermore, it has been pointed out that the provision of a fixing mechanism makes the recording device complicated. In addition, the fixation time is rate-limiting for the process, so that it becomes impossible to make the best use of the quick drying property that is the advantage of the hot-melt ink composition.
The present inventors have proposed hot-melt ink compositions described in U.S. Pat. No. 5,000,786, Japanese Patent Laid-Open No. 277910/1988 and European Patent No. 0315406. The present invention provides a hot-melt ink composition improved over these hot-melt ink compositions.